1. Field of the Invention
This invention relates to improvements in fluid pumping apparatus and, more particularly, it concerns a peristaltic pump system which is adaptable to a wide range of applications in which reliably accurate rates of fluid delivery are required over extended periods of time.
2. Description of the Prior Art
Peristaltic pumps are well known and may be characterized generally as that class of fluid pumps in which a fluid pressure differential is created by alternately compressing and expanding an elastic tube. Typically, peristaltic pumps include a continuous length of tubing extending between an intake end at a source or supply of fluid and a discharge end in fluid communication with the point to which fluid is to be pumped. The pumping pressure differential resulting in movement of fluid through the elastic tube is brought about by progressively pinching the tube either by means such as a pinch roller movable relative to the tube while it is fixed against movement or by advancing the tube through a fixed nip defined by a pinch roller pair, for example. In either case, pressure is developed in the tube in advance of the progressive point of pinching and suction results in the tubing behind the same point as a result of the tubing returning to an expanded condition under the elastic memory of the material from which it is formed.
Because most pumping systems transfer fluids between fixed points of fluid supply and fluid discharge, peristaltic pumps most commonly employ a fixed length of elastic tubing and one or more compression rollers driven in orbital fashion to traverse an arcuate segment of the tubing. The disclosure of U.S. Pat. Nos. 3,527,220; 3,674,383 and 3,972,649 are representative of this type of peristaltic pump. As is apparent from the disclosure of the first two of these patents, a principal advantage of this type of peristaltic pump is that the entire flow path from the intake to the discharge end of the tubing is constituted exclusively by the tubing itself, thus eliminating any need for fittings, joints and other such hardware. Two basic problems, however, are presented by the fixed tubing of such pumps. In the first place, the requirement for the pressure developing roller to be driven in orbital fashion contributes to difficulties in maintaining an accurately constant rate of movement in the compression roller. Secondly, the same length of tubing is continuously contracted and expanded with the result that the effective life of the pump is limited by the continued ability of the tubing to expand under the elastic memory of the material from which it is formed. This latter problem is addressed in the disclosure of the third of the above-cited patents (U.S. Pat. No. 3,972,649) where a coiled supply of the tubing is provided to allow for the compressing pumping action to take place along the length of the tubing. The overall simplicity of the basic pump class, however, is compromised by the relatively complicated additional hardware required.
U.S. Pat. Nos. 2,960,868 and 3,327,898 are representative of a different type of peristaltic pump in which the tubing is moved relative to the nip of a fixed pinch roller. The earlier of these two patents relates to a pipette pump in which extremely small quantities of fluid are handled and which relies on movement of the tubing from a loop having one end fixed. The latter of the two patents discloses a similar apparatus in which the tubing constitutes the sole supply of fluid pumped. In this instance, the tubing is supplied as convolutions on a spool rotated relative to a fixed pinch roller. The pinch roller traverses the serveral convolutions of the tubing to discharge only fluid contained in the tubing. It is apparent that while the pumps disclosed in both of these latter patents are capable of very accurate pumping rates, neither is intended for operation without interruption over extended periods of time.
The cited U.S. Pat. No. 3,527,220, as well as U.S. Pat. No. 3,496,878 are further representative of pumping systems designed to be implanted in an animal body for the administration of drugs. Peristaltic pumps are especially suited to this particular application out of such inherent characteristics as facility for sterilization, predictability of pumping capacity by selection of the tubing size, overall simplicity, and facility for incorporation in a relatively small package. On the other hand, the application, in itself, demonstrates an acute need for reliability of operation over extended periods of time, capability for accurate control of pumping rates, and adaptability to severe packaging constraints.